The graph below shows the transverse velocity $u$ as function of time of the point on a string at $x=0,$ as a wave passes through it$.$ The scale on the vertical axis is set by $u_s=4\frac{m}{s}.$

The wave has the form $y(x,t)=$Asin$(kx-t+).$ What is the $($positive$)$ value of $($in degrees$)?$

$($You should get a negative $,$ add $360$ to get the positive angle.$)$

Hint: Check your answer by substituting $$ and assumed value of $$ into $y(x,t)$ and then plotting the function.